1. Field of the Invention
The present invention relates to orthopedic prostheses designed to support muscles in the human shoulder and, more particularly, to such a prosthesis designed to reduce the strain on shoulder muscles during a full range of arm movements by aiding movement of the arm.
2. General Background
The human shoulder is particularly susceptible to pull, tear and strain of certain muscle groups and connecting tendons and ligaments. These injuries lead to decreased function of the shoulder during the period of recovery and, in severe cases, can result in a permanent decrease in shoulder function. The decrease in function may occur as a result of a traumatic incident such as a muscle or ligament tear, or may occur as a result of disease or atrophy of the shoulder muscles due to age or other causes. Such injuries are particularly serious for athletes who rely on arm and shoulder movement in order to perform. When there is a slight tear or pull, an athlete should refrain from any strenuous activity. Attempts to make the shoulder function at previous levels of performance before a total recovery can often result in re-injury or an aggravation of the injury.
A common approach in dealing with this tendency to re-injure the shoulder muscles has been to deliberately restrict movement during the recovery or healing period. A number of devices have been designed to restrict movement during this period. Examples of such devices include those described in the following U.S. patents.
U.S. Pat. No. 3,906,944 describes a shoulder harness which limits the range of arm movement to less than 90 degrees away from the body by limiting the degree to which shoulder muscles abduct or contract.
U.S. Pat. No. 4,644,939 describes a shoulder brace for limiting and guiding movement of the arm as it is raised from the wearer's side. An elasticized brace is described as limiting upward movement of the arm by "anchoring" the upper arm to the wearer's body through an elasticized web. The web applies tension on the upper arm, which is described as limiting the arm's movement and guiding the humerus in its movement within the shoulder socket.
U.S. Pat. No. 3,499,441 also describes an elasticized brace which restricts movement through use of elastic bands surrounding the shoulder, limiting both lateral movement of the shoulder and the range of movement of the arm from the wearer's side.
U.S. Pat. No. 559,024 describes an elasticized body brace that includes woven and elastic material for limiting the range of movement of the arm and shoulder.
None of the above devices included any features that actually aid in arm movement. One device that does aid movement of the arm is described in U.S. Pat. No. 4,180,870 where a wearer harness and pneumatic energizing means helps the wearer lift his or her arm through a system of levers and eccentric cams for articulating the arm toward and away from the body of the wearer. While this device assists in movement of the shoulder, arm and wrist, it is a cumbersome device to wear, expensive to manufacture and has the effect of limiting rate of movement to a predetermined rate of movement of a hydraulic cylinder.